1. Field of the Invention
The present invention relates to a method for recovering dry solid powder from highly concentrated, high viscous solutions.
2. Discussion of the Related Art
Difficulties in recovering dry solid particles from highly concentrated, high viscous, semi-liquids solutions are known in the art. In particular, such difficulties arise when the solids present in the solution constitute a mixture and not a pure substance, as often occurs in the processing of substances from natural sources. In situations like that, the solute does not crystallize easily, preventing simple separation. For example, it is well known that solutions of sugar mixtures (i.e., molasses) and especially those which contain oligosaccharaides, are very difficult to crystallize. Recovery of the solids by means of solvent evaporation also fails many times to give pure and fine solid particles, since small amounts of liquid are entrapped between the amorphous solid skeleton. Thus, evaporation often results either in a dough-like substance which cannot be dried further or in one lump of hard solid which is difficult to handle and needs to be further pulverized. Furthermore, soluble contamination remains entrapped in the dried solid so obtained. Moreover, complete evaporation often requires high temperatures which might destroy the substances to be recovered. In other cases, the solvent itself decomposes or undergoes chemical reactions before it reaches boiling temperature. In such cases, where complete evaporation is impossible, due to destruction of the solvent, removal of solvent can be performed by multi-stage solvent extraction. For example, in the de-oiling process of commercial lecithin, vegetable oil is removed by multi-stage solvent extraction.
However, for most applications dry solid powder is preferable to a concentrated solution. Powders have prolonged shelf life, are easier to handle and to pack and consequently are cheaper to transport, while liquids, having higher volume and weight, impose packaging and leakage problems. Moreover, preparing solutions from powder impose no difficulties, such that powder can be used as is or can be easily turned into a solution if required. For some applications, only dry material can be used. In particular, when relating to food additives, syrup-like additives are limited to xe2x80x9cwet-foodsxe2x80x9d and cannot be used for powdered foodstuff.
Known methods for obtaining dry solid particles from syrup-like, semi-liquid highly concentrated solutions include spray drying, vacuum freeze-drying and solvent extraction. However, these methods require sophisticated and expensive equipment, are high energy consuming or need large solvent quantities, and the results are not always satisfactory. No further purification is achieved by the drying methods and in many cases, the particles formed tend to stick onto the equipment walls and to clog equipment passages, making the process cumbersome and time consuming. Moreover, in order to spray dry or freeze dry, the concentrated solutions need to be diluted to a much lower concentration, thus these processes are energy consuming as well. There is therefore a need for a simple and better way for recovering solid powder from highly concentrated viscous solutions.
The present invention provides an essentially one-step, simple and economical method for obtaining a purified solid powder from a highly concentrated viscous solution. The process requires relatively simple equipment and common cheap materials.
In accordance with the present invention, there is thus provided an economical method for obtaining purified solid substance, in the form of a fine powder, from a highly concentrated viscous solution containing a solute and a first solvent. The solute may be a pure substance or a mixture of substances, the first solvent may be a pure solvent comprising a single compound or a mixture of solvents.
The present method comprises subjecting the highly concentrated viscous solution to a second solvent under conditions of high shear mixing, wherein the second solvent is miscible with the first solvent and wherein the solute to be recovered has a very low solubility or no solubility at all in said second solvent, whereby a suspension of purified fine particles is obtained. The suspension can be easily separated by filtration for obtaining a fine powder of the solid substance. The high shear mixing may be performed by means of a high-performance dispersion instrument (e.g., Ultra-Turrax), a high speed mixer (e.g., high speed blender), or by any other means suitable for generating high shear mixing forces. The process of the present invention may be performed either batchwise or continuously.
In accordance with one embodiment of the present invention the highly concentrated viscous solution is a honey-like commercial lecithin, the first solvent is vegetable oil and the second solvent is acetone. According to this embodiment, the process is aimed at de-oiling the commercial lecithin for obtaining de-oiled lecithin powder. Preferably, the amount of acetone added to commercial lecithin is such that the acetone: lecithin weight ratio is in the range of 2:1 to 5:1.
In accordance with another embodiment of the present invention the highly concentrated viscous solution is an aqueous solution of one or more saccharaides (i.e., the first solvent is water), wherein the second solvent is absolute ethanol. The process is especially suitable for obtaining purified saccharaide powder from molasses of natural sources which contain oligosaccharaides, such as soybean molasses. Preferably, absolute ethanol is added to the molasses in an amount such that the weight ratio between the ethanol and the sugars contained in said molasses is in range of 13:1 to 20:1.
The present invention provides a method for recovering a solid substance in the form of fine particles from highly concentrated syrup-like or honey-like solutions, or, in other words, a method for separating the solute/solutes from the solvent. Given that the solution is highly concentrated, the process may be considered as extracting the solvent (referred to as the first solvent) from the solute.
The method of the present invention is essentially a one-step process in which a second solvent is added to the highly concentrated solution while subjecting the mixture to high shear mixing, to obtain a suspension of fine particles in a liquid phase consisting of the first and the second solvents. The second solvent is selected to fulfill the following requirements: a) it is highly miscible with the solvent contained in the concentrated solution (i.e., the solvent to be extracted); and b) the solute (i.e., the solid to be recovered) has a very low solubility or no solubility at all in it. Under the high shear forces a suspension of fine particles is immediately obtained (i.e., a few seconds or parts of seconds), from which the solids can be easily separated by filtering.
In accordance with the present invention, the high shear mixing can be performed by means of a high shear mixing apparatus or a high-performance dispersing apparatus and the process may be performed either batchwise or continuously by using suitable equipment.
The present method is preferred to other methods, such as spray drying, complete evaporation or multistage solvent extraction, since it is simple, does not require complicated equipment and the solids are obtained as dry, non-sticky pure powder which does not adhere to equipment walls and does not cause clogging problems. Moreover, this method leaves foreign substances in the solution, resulting in purer solid particles, unlike evaporation methods in which contaminations are entrapped within the solid particles.
The present invention will be further described and explained by the following examples. It will be easily appreciated that these examples do not intend to be limiting but rather to illustrate and demonstrate the invention.
A: De-Oiled Soy Lecithin Powder from Commercial Soy Lecithin
Commercial soy lecithin is a byproduct of the water degumming process of crude soybean oil in the soybean solvent extraction process. The commercial soy lecithin is obtained after water removal, and is a honey-like substance consisting of about 50-80% acetone insoluble (A.I.) phospholipids, up to one percent water, and the rest is soy oil. The main A.I components of commercial lecithin are the phospoholipids phosphatdylcholine, phospatdylethanolamine and phosphatdylinositol
The following two examples demonstrate a process for de-oiling commercial soy lecithin for obtaining powdered de-oiled soy lecithin of high A.I. content.